In known active matrix display devices, a plurality of pixels arranged in a matrix include the respective switches. Each pixel performs display in accordance with a desired potential (image signal) input through the switch.
Active matrix display devices require circuits (scan line driver circuits) that control switching of switches provided in respective pixels by controlling the potentials of scan lines. A general scan line driver circuit includes n-channel transistors and p-channel transistors in combination; however, it is also possible to form a scan line driver circuit using either n-channel transistors or p-channel transistors. Note that the general scan line driver circuit in the former case can have lower power consumption than the scan line driver circuit in the latter case. On the other hand, the scan line driver circuit in the latter case can be formed through a smaller number of manufacturing steps than the general scan line driver circuit in the former case.
When a scan line driver circuit is formed using either n-channel transistors or p-channel transistors, a potential supplied to a scan line changes from a power supply potential supplied to the scan line driver circuit. Specifically, when a scan line driver circuit is formed using only n-channel transistors, at least one n-channel transistor is provided between a scan line and a wiring that supplies a high power supply potential to the scan line driver circuit. In this case, a high potential supplied to the scan line is lower than the high power supply potential by the threshold voltage of the at least one n-channel transistor. In a similar manner, when a scan line driver circuit is formed using only p-channel transistors, a low potential supplied to the scan line is higher than a low power supply potential supplied to the scan line driver circuit.
In response to the above problem, it has been proposed to provide a scan line driver circuit which is formed using either n-channel transistors or p-channel transistors and which can supply, to a scan line, a power supply potential supplied to the scan line driver circuit, without a change.
For example, a scan line driver circuit disclosed in Patent Document 1 includes an n-channel transistor that controls electrical connection between scan lines and clock signals alternating between a high power supply potential and a low power supply potential at evenly spaced periods. When the high power supply potential is supplied to a drain of the n-channel transistor, a potential of a gate thereof can be raised owing to the capacitive coupling between the gate and a source thereof. Thus, in the scan line driver circuit disclosed in Patent Document 1, the same or substantially the same potential as the high power supply potential can be supplied from the source of the n-channel transistor to the scan lines.
The number of the switches provided in each pixel arranged in an active matrix display device is not limited to one. Some display devices include a plurality of switches in each pixel and control the switchings of the switches separately to display an image. For example, Patent Document 2 discloses a display device including two kinds of transistors (a p-channel transistor and an n-channel transistor) in each pixel, and the switchings of the transistors are controlled separately by different scan lines. In order to control the potentials of the separately provided two kinds of scan lines, two kinds of scan line driver circuits (a scan line driver circuit A and a scan line driver circuit B) are further provided. In the display device disclosed in Patent Document 2, the separately provided scan line driver circuits output signals having substantially opposite phases.
As disclosed in Patent Document 2, there also exists a display device in which a scan line driver circuit outputs, to one of two kinds of scan lines, inverted or substantially inverted signals of signals output to the other of the two kinds of scan lines. Such a scan line driver circuit is formed using either n-channel transistors or p-channel transistors. For example, the scan line driver circuit disclosed in Patent Document 1, which outputs signals to the scan lines, may output the signals to one of the two kinds of scan lines and to an inverter, and the inverter may output signals to the other of the two kinds of scan lines.